The present invention relates in general to a photometric apparatus for a microscope, which measures the brightness of a microscopic image, and calculates and determines an exposure time for photographic imaging in accordance with the measured brightness.
Conventionally, microscopes capable of observing minute samples, photographing an observed image or recording a video image have been used in a variety of areas ranging from biological researches to industrial inspections. In particular, in cases of photographing and recording observation images, photographing devices custom-designed for microscopes are normally used. The photographing devices for microscopes are generally provided with so-called automatic exposure functions for measuring the brightness of observation images and automatically calculating exposure time in accordance with the measured brightness. As regards the conventional structure for the automatic exposure function, a light-reception element (a photo electric element, a photo detector) in a section for measuring the brightness of an observation image, that is, a photometric area, has a fixed shape.
Observation images acquired by microscopes, however, have various shapes depending on observation methods or subjects (samples). If only a fixed area is photometrically measured, an optimal exposure time cannot be obtained. For example, depending on the types of microscopes, there are many cases where samples are distributed only in ranges less than photometric areas (light-reception areas). If such a sample is photographed by the conventional photometric method, the following problems will arise: light is radiated only on an area less than a photometric area (light-reception area), and the other area is treated as a background. This background has a lower brightness in the case of fluorescence observation, etc., and has a higher brightness in the case of bright-field observation, etc.
If a photometric operation is performed under the above-described condition, a total luminance is averaged by the light-reception area and the sample will disappear in the background. Consequently, the actual exposure time will become longer than an optimal exposure time in the case of fluorescence observation, and become shorter than the optimal exposure time in the case of bright-field observation. As a result, the observation image, which is actually desired, will not clearly appear on the produced photograph due to excessive or deficient exposure, and the photographing will fail. Various techniques have been proposed to solve the problems.
Jpn. U.M. Appln. KOKAI Publication No. 61-144443 shows a structure wherein partial photometry and average photometry are mechanically (optically) switched to selectively extract a necessary area of an observation image, and the selected area can be shifted to a desired position within a view field of a microscope to achieve optimal exposure. On the other hand, Jpn. Pat. Appln. KOKAI Publication No. 56-155820 discloses a technique relating to devised calculation of luminance information, wherein a photometric measurement area is divided into a number of portions and the respective associated luminance values are weighted.
Moreover, Jpn. Pat. Appln. KOKAI Publication No. 6-222282 proposes a technique wherein attention is paid, in particular, to the above-mentioned fluorescent sample. According to this technique, a two-dimensional CCD imager is used to achieve optimal exposure even where luminance varies from point to point and there is a large difference in luminance between a necessary area for photometry and the background. Jpn. Pat. Appln. KOKAI Publication No. 7-168103 relates to an improvement of this technique, wherein partial photometry can be performed in any area within the view field of the microscope. Since photometry can be performed by designating a desired location within the view field of the microscope, irrespective of the luminance distribution or locations of samples, optimal exposure time can be calculated for any sample.
As has been described above, there are many proposals for achieving optimal exposure and the photographing apparatuses have been improved.
According to the system of Jpn. U.M. Appln. KOKAI Publication No. 61-144443, however, the mechanical switching of the photometric measurement area makes the structure complex, and the operability for assembly and adjustment is considerably low. In addition, since mechanical movable members are employed, slide surfaces are abraded and contaminant, which is most detrimental to the optical system, will occur. This may adversely affect the photometry or observation system.
In the techniques of Jpn. Pat. Appln. KOKAI Publication No. 56-155820, Jpn. Pat. Appln. KOKAI Publication No. 6-222282 and Jpn. Pat. Appln. KOKAI Publication No. 7-168103, a drive circuit, a data take-in circuit, etc. for taking in data from divided pixels are required and the structure relating to electrical components is complicated. As a result, the size and manufacturing cost of the apparatus will increase.
In particular, where the CCD imager is used as in Jpn. Pat. Appln. KOKAI Publication No. 6-222282, exact photometric operations cannot be performed unless the output characteristics of respective pixels are uniformly corrected. An additional adjustment mechanism for correcting variance is required and the manufacturing cost of the apparatus will further increase. Furthermore, in the technique of Jpn. Pat. Appln. KOKAI Publication No. 7-168103, like Jpn. U.M. Appln. KOKAI Publication No. 61-144443, there are many mechanical drive components and problems of contamination will arise.
It is well known that when an optical system is assembled, the optical axis of the optical system needs to be aligned. When the conventional CCD imager is used, too, the alignment is performed while checking electric signals.
As has been described above, in the conventional photographing apparatuses for microscopes, the mechanical structure and electric circuits are complex and involve an increase in size. Consequently, the adjustment and assembly of the apparatus becomes more difficult, and the manufacturing cost of the apparatus increases.
The object of the present invention is to provide a photometric apparatus for a microscope, wherein operability for assembly and adjustment can be enhanced with low cost, and the precision of photometry is increased.
In order to achieve the object of the invention, there is provided a photometric apparatus for a microscope, the apparatus comprising: a light-reception element having a plurality of concentrically arranged photometric measurement areas, the light-reception element receiving observation light from the microscope and measuring a brightness of an observation image of the observation light; a calculation circuit for calculating an exposure time necessary for photographing the observation image, on the basis of a photometric measurement value obtained from at least one of the plurality of photometric measurement areas of the light-reception element; and a control circuit for performing an exposure operation on the basis of the exposure time calculated by the calculation circuit.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.